Laser-induced optical wiring apparatus

ABSTRACT

A laser-induced optical wiring apparatus includes a substrate, first and second light-reflecting members provided on the substrate separately from each other, an optical waveguide provided on the substrate for optically coupling the first and second light-reflecting members to form an optical resonator, a first optical gain member provided across the optical waveguide and forming a laser oscillator along with the first and second light-reflecting members, and a second optical gain member provided across the optical waveguide separately from the first optical gain member, and forming another laser oscillator along with the first and second light-reflecting members.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional application of Ser. No. 11/531,936filed Sep. 14, 2006, which is based upon and claims the benefit ofpriority from prior Japanese Patent Application No. 2005-323666, fieldNov. 8, 2005, the entire contents of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a laser-induced optical wiringapparatus in which optical wiring is realized by a laser oscillator.

2. Description of the Related Art

Drastic enhancement of the operation speed of LSIs has been achieved bythe enhancement of performance of electronic devices, such as bipolartransistors and field effect transistors. However, while the performanceof electronic devices is enhanced by the microfabrication oftransistors, the wiring resistance or inter-wiring capacitance in thedevices is increased as a result of the microfabrication. The increasesin the wiring resistance or inter-wiring capacitance are becoming abottleneck in the increase of the performance of LSIs.

In consideration of such a problem in electric wiring as the above,several optical wiring LSIS, in which light is used to connect elementsin the LSIs, have been proposed (see, for example, JP-A H6-132516(KOKAI). Optical wiring is almost free from the dependency of loss uponfrequency regardless of whether the current supplied thereto is a directcurrent or an alternating current of 100 GHz or more, and from disorderin wiring paths due to electromagnetism.

However, such a conventional technique as that of JP-A H6-132516 (KOKAI)exhibits significantly low reproducibility and reliability if it isapplied to LSIs with an extremely large number of wires. For instance,even if it is assumed that optical wiring is employed only for theuppermost layer (global layer) of LSI wiring, one LSI chip may wellinclude several hundreds of optical wires. In this case, to operate oneLSI, it is necessary to operate several hundreds of optical wires withall the wires kept in good condition. In light of the manufacturingyield of LSIs, this means that reproducibility and reliability arerequired for the production technique, which enable no single defectiveoptical wire to be contained in several tens of thousands to severalhundreds of thousands of optical wires produced. Thus, each optical wirefor LSIs must have extremely high reproducibility and reliability. Tothis end, each optical wire must have an extremely simple structure andan extremely small size for highly integration.

Basically, a light-emitting element, optical waveguide andlight-receiving element are essential elements for the conventionaloptical wiring. Accordingly, light-emitting element techniques,light-receiving element techniques and optical waveguide techniques arenecessary. It is also necessary to make a complete survey of varioustechniques including peripheral techniques, such as optical couplingtechniques for efficiently optically coupling the light-emitting elementto the light-receiving element, and optical transmission systemdesigning techniques. Moreover, those basic elements differ from eachother in operation principle, material, structure, processing technique,and hence it is necessary to delicately combine materials and processingtechniques to form optical wiring. This process is extremely difficultto realize.

As described above, in conventional optical wiring techniques, since thestructural elements are very complex, and various materials must be usedto form the elements, problems will easily occur in the stability orreproducibility of the characteristics. Furthermore, it is difficult toreduce the size of the wiring. Thus, the conventional optical wiringtechniques include a large number of unsuitable factors for LSI wiring.

BRIEF SUMMARY OF THE INVENTION

In accordance with a first aspect of the invention, there is provided alaser-induced optical wiring apparatus comprising:

a substrate;

a first light-reflecting member and a second light-reflecting member,which are provided on the substrate separately from each other;

an optical waveguide provided on the substrate, the optical waveguideoptically coupling the first light-reflecting member and the secondlight-reflecting member to form an optical resonator;

an optical gain member provided across a portion of the opticalwaveguide and forming a laser oscillator along with the firstlight-reflecting member and the second light-reflecting member; and

an optical switch provided across a portion of the optical waveguideseparately from the optical gain member, the optical switch performing aswitching operation to change a loss of an optical path extendingbetween the first light-reflecting member and the secondlight-reflecting member in accordance with an input signal to change alaser oscillation state of the laser oscillator.

In accordance with a second aspect of the invention, there is provided alaser-induced optical wiring apparatus comprising:

a substrate;

a first light-reflecting member and a second light-reflecting member,which are provided on the substrate separately from each other;

an optical waveguide provided on the substrate, the optical waveguideoptically coupling the first light-reflecting member and the secondlight-reflecting member to form an optical resonator;

a first optical gain member provided across a portion of the opticalwaveguide and forming a first laser oscillator along with the firstlight-reflecting member and the second light-reflecting member; and

a second optical gain member provided across a portion of the opticalwaveguide separately from the first optical gain member, and forming asecond laser oscillator along with the first light-reflecting member andthe second light-reflecting member.

In accordance with a third aspect of the invention, there is alaser-induced optical wiring apparatus comprising:

a substrate;

a first light-reflecting member and a second light-reflecting member,which are provided on the substrate separately from each other;

a third light-reflecting member and a fourth light-reflecting member,which are provided on the substrate separately from each other;

a first optical waveguide provided on the substrate, the first opticalwaveguide optically coupling the first light-reflecting member and thesecond light-reflecting member to form a first optical resonator;

a first optical gain member provided across the first optical waveguideand forming a first laser oscillator along with the firstlight-reflecting member and the second light-reflecting member;

a second optical gain member provided across the first optical waveguideseparately from the first optical gain member, and forming a secondlaser oscillator along with the first light-reflecting member and thesecond light-reflecting member;

a second optical waveguide provided on the substrate perpendicularly tothe first optical waveguide, the second optical waveguide opticallycoupling the third light-reflecting member and the fourthlight-reflecting member to form an optical resonator;

a third optical gain member provided across the second optical waveguideand forming a laser oscillator along with the third light-reflectingmember and the fourth light-reflecting member; and

a fourth optical gain member provided across the second opticalwaveguide separately from the third optical gain member, and forming alaser oscillator along with the first light-reflecting member and thesecond light-reflecting member.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a schematic perspective view illustrating the structure of alaser-induced optical wiring apparatus according to a first embodiment;

FIG. 2 is a schematic sectional view illustrating the structure of thelaser-induced optical wiring apparatus of the first embodiment;

FIG. 3 is a view useful in explaining the operation of the firstembodiment;

FIG. 4 is another view useful in explaining the operation of the firstembodiment;

FIG. 5 is yet another view useful in explaining the operation of thefirst embodiment;

FIG. 6 is a graph illustrating laser oscillation characteristic examplesof the laser-induced optical wiring apparatus of the first embodiment;

FIG. 7 is a circuit diagram illustrating a laser-induced optical wiringapparatus according to a second embodiment, which includes a circuitequivalent to the apparatus of FIG. 1, and a peripheral circuit;

FIG. 8 is a schematic perspective view illustrating the structure of alaser-induced optical wiring apparatus according to a third embodiment;

FIG. 9 is another schematic perspective view illustrating the structureof the laser-induced optical wiring apparatus of the third embodiment;

FIG. 10 is a schematic perspective view illustrating the structure of alaser-induced optical wiring apparatus according to a fourth embodiment;

FIG. 11 is a schematic perspective view illustrating the structure of alaser-induced optical wiring apparatus according to a fifth embodiment;

FIG. 12 is a sectional view illustrating the structure of thelaser-induced optical wiring apparatus according to the fifthembodiment;

FIG. 13 is a sectional view illustrating the structure of an opticalguide portion employed in the fifth embodiment, and a waveguide modeoccurring in the guide portion;

FIG. 14 is a sectional view illustrating the structure of anotheroptical guide portion employed in the fifth embodiment, and a waveguidemode occurring in the guide portion;

FIG. 15 is a sectional view illustrating the structure of a modificationof the invention; and

FIG. 16 is a sectional view illustrating the structure of anothermodification of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The gist of the present invention does not lie in one-way lighttransmission operation, but lies in that a light emitting element,optical waveguide and another light emitting element are spatiallydistributed and made to cooperate to serve as a single system includingtwo single laser oscillators, and each laser operation of the system istransmitted as a signal. Namely, utilizing the fact that when there isan operation slower than the standard operation speed of the system,this operation is instantly transmitted to the whole system,transmission of a signal to a spatially separate place is realized. Atthis time, one of the light emitting elements is made to function as anoptical switch for controlling the optical gain (or loss) of the systemincluding the two laser oscillators, and the other element is made tofunction as a receiver for receiving and transmitting, to the outside,variations in, for example, excited carriers corresponding to variationsin the optical amount of the whole system.

A detailed description will be given of the present invention, using theembodiments shown in the accompanying drawings. In the embodiments,several specific materials are employed. However, the invention is notlimited to them. It is sufficient if the material can perform laseroscillation. Accordingly, the invention is not limited to theembodiments described below. Further, in the embodiments, one or twooptical wires are described. Actually, however, a large number ofoptical wires are integrated on an LSI chip. Any arbitrary number ofoptical wires may be employed.

First Embodiment

FIG. 1 is a schematic perspective view illustrating the structure of alaser-induced optical wiring apparatus according to a first embodiment.FIG. 1 shows only elements necessary for optical wiring. Further, FIG. 2shows the cross section taken along the axis of the apparatus of FIG. 1.Although the first embodiment employs GaInAsP/InP-based materials asmaterial examples of the apparatus, it may employ other materials, suchas GaAlAs/GaAs-based materials, Si and SiGe/Si.

In FIGS. 1 and 2, reference number 11 denotes an n-type InP substrate,reference numbers 12 a and 12 b denote GaInAsP active layers (lasermedium having an emission wavelength of 1.3 μm), reference number 13denotes a GaInAsP optical waveguide core (having, for example, a bandgap wavelength of 1.2 μm), reference numbers 14 a and 14 b denote p-typeInP layers, and reference number 15 denotes a semi-insulated clad layer(e.g., an Fe-doped InP layer). Further, reference numbers 16 a and 16 bdenote p-side electrodes (formed of, for example, AuZn), referencenumber 17 denotes an n-side electrode (formed of, for example, AuGe),and reference numbers 18 a and 18 b denote mirrors formed by dryetching.

On the InP substrate 11, the GaInAsP optical waveguide core 13 formed tostripe, and semi-insulated clad layer 15 covers the stripe and theperiphery. The mirrors 18 a and 18 b are formed by dry-etching theopposite ends of the stripe structure. The GaInAsP active layers 12 aand 12 b are provided near the opposite ends of the optical waveguidecore 13, and the p-type InP layers 14 a and 14 b are provided near theopposite ends of the semi-insulated clad layer 15.

The p-side electrodes 16 a and 16 b are provided on the InP layers 14 aand 14 b, respectively, and the n-side electrode 17 is provided on thelower surface of the substrate 11. Namely, an optical waveguide (opticalwaveguide core 13) is formed, connecting the mirrors 18 a and 18 b toeach other. A first optical gain section (active layer 12 a) and asecond optical gain section (active layer 12 b) that forms a laseroscillator along with the mirrors 18 a and 18 b and optical waveguidecore 13. Assume here that each active layer 12 has, for example, athickness of 0.12 μm, a width of 1 μm, and a length of 50 μm. Further,assume that the optical waveguide core 13 has, for example, a thicknessof 0.12 μm, a width of 1 μm, and a length of 1 mm. The active layers 12and optical waveguide core 13 may have a quantum well structure. Thelength of the optical waveguide core 13 serves as a parameter fordetermining the maximum operation frequency of the laser oscillator, ifit is longer than a certain value, the operation speed of the opticalwiring apparatus is limited. This will be explained later.

As shown in FIG. 2, the active layers 12 a and 12 b are directlyconnected to the optical waveguide core 13, and the layers 12 a and 12 bare optically coupled to each other. The active layers 12 a and 12 b andoptical waveguide core 13 may be sequentially formed by crystal growthand patterning. Alternatively, firstly, crystal growth may be made usinga composition control technique using selective growth, such as amulti-quantum-well structure, and then the resultant structure bepatterned into the layers 12 a and 12 b and core 13. Further, themirrors 18 a and 18 b having perpendicular end faces are provided at theouter ends of the active layers 12 a and 12 b, thereby forming aso-called fabry-Perot oscillator. In the first embodiment, basically, itis not necessary to output light to the outside of the apparatus.Therefore, the mirror reflectance may be enhanced by providing theperpendicular end faces with high reflection coating or metal coating(not shown).

Further, instead of dry-etching the outer ends of the active layers 12 aand 12 b, an extended optical waveguide with a diffraction grating maybe provided to form a distributed Bragg reflector (DBR) laser structure.Alternatively, a diffraction grating may be provided near the upper,lower, left or right portion of each active layer 12 a, 12 b to form adistributed feedback (DFB) laser structure. When the DFB laser structureis employed, even only one of the active layers 12 a and 12 b canoscillate in principle. However, to realize a cooperative operation ofthe active layers 12 a and 12 b, the oscillation threshold value foreach active layer is set relatively high. The operation principle of thelaser-induced optical wiring apparatus constructed as the above will benow be described.

FIGS. 3 and 4 are views useful in explaining the operation of thelaser-induced optical wiring apparatus. In each of FIGS. 3 and 4, theupper portion is a schematic sectional view mainly showing the activesection of the laser-induced optical wiring apparatus, the middleportion shows an internal light intensity distribution, and the lowerportion shows an equivalent circuit. Reference numbers 12 a and 12 bdenote the laser active layers, reference number denotes the opticalwaveguide core, and reference numbers 18 a and 18 b denote thereflection mirrors.

When only the active layer 12 a is activated (i.e., a current is flowninto only the layer 12 a), the internal light intensity (E) exhibits agentle attenuation distribution curve between the active layer 12 a andthe optical waveguide 13, as is shown in FIG. 3. However, abrupt lightabsorption occurs, i.e., abrupt light attenuation occurs, in the activelayer 12 b that has the same band-gap as the active layer 12 a. To makethe system in this state perform laser oscillation, it is necessary tostrongly activate the active layer 12 a until the active layer 12 a ismade transparent by optical activation. This process, however, is veryhard to execute. In contrast, when only the active layer 12 b isactivated as shown in FIG. 4, a light distribution opposite to that ofFIG. 3 is acquired. Of course, it is also difficult to perform laseroscillation in this state.

When both the active layers 12 a and 12 b are activated as shown in FIG.5, a substantially uniform internal light distribution is acquired,i.e., the gain of light acquired when light makes a circuit of thesystem can be set to 1. Namely, laser oscillation is possible. Assumehere that the reflectance of the mirror 18 a (located closer to theactive layer 12 a), the reflectance of the mirror 18 b (located closerto the active layer 12 b), the length of the active layer 12 a, thelength of the active layer 12 b, the induction emission gain of theactive layer 12 a, the induction emission gain of the active layer 12 b,the absorption loss of the active layer 12 a, the absorption loss of theactive layer 12 b, the length of the optical waveguide 13, theabsorption loss of the optical waveguide 13, the coupling coefficientbetween the active layer 12 a and optical waveguide 13, and the couplingcoefficient between the active layer 12 b and optical waveguide 13 areused as characteristic parameters Ra, Rb, La, Lb, ga, gb, αa, αb, Lt,αt, Ca and Cb, respectively. In this case, the laser oscillationcondition for the entire system is that under which light can maintainits original intensity even after making a circuit of the system.Namely, the following equation must be satisfied:ln{1/(Ra×Rb×Ca×Ca×Cb×Cb)}=2(ga×La+gb×Lb−αa×La−αb×Lb−αt×Lt)  (1)where ga and gb are functions concerning carriers (current) injectedinto the active layers 12 a and 12 b, and the other parameters are fixedif the structure is fixed. Accordingly, the laser oscillation conditionis that the optical gain based on ga and gb exceeds the optical loss ofthe system. It is sufficient if the following relationship isestablished:ga(Ifa)La+gb(IFb)Kb=αa×La+αb×Lb+αt×Lt+[ln{1/(Ra×Rb×Ca×Ca×Cb×Cb)}]/2  (2)where IFa and IFb represent activation currents for the active layers 12a and 12 b, respectively.

FIG. 6 shows laser oscillation characteristic examples assumed when anSiO₂/Si multi-layer is coated on the perpendicular-end-face mirrors 18 aand 18 b in the structure of FIG. 1. In the examples, Ra=Rb=80%.Further, IFa=IFb=IF/2, i.e., the same current is flown through thelayers 12 a and 12 b.

In FIG. 6, the abscissa indicates the element voltage (VF) and theoptical output (Po) from each mirror end face, while the coordinateindicates the sum (IF=IFa+IFb) of the currents flown through the activelayers 12 a and 12 b. In FIG. 6, two lines of Po indicate the case wherethe system of FIG. 1 performs laser oscillation, and the case where thesystem does not perform laser oscillation. Similarly, the two lines ofVF indicate those cases. The characteristics corresponding to no laseroscillation are acquired by interrupting optical coupling of the activelayers 12 a and 12 b by non-perpendicular etching of the middle of theoptical waveguide 13. In any case, the electrical characteristics of theactive layers 12 a and 12 b do not change.

In FIG. 6, the point at which Po abruptly increases indicates thethreshold values for laser oscillation. Specifically, the thresholdvalues are the current threshold value Ith, and the voltage thresholdvalue Vth. FIG. 6 shows the characteristics acquired when symmetricalactivation of IFa=IFb is performed. If IFa≠IFb, the resultant currentand voltage threshold values may well be deviated from Ith and Vth inFIG. 6 because of the nonlinear characteristic of gain g (IF).

The active layers 12 a and 12 b serve as diodes held between the p-typeclad layers 14 a and 14 b and the n-type clad layer (substrate) 11,respectively, and their current/voltage characteristic is given byI=I0[exp{(V−I×Rs)e/n×k×T}  (3)where Rs is the internal resistance of a pn-junction diode formed of theelements 16 a (or 16 b), 14 a (or 14 b), 12 a (or 12 b), 11 and 17, I0is a saturation current, n is a constant for the diode, k is theBoltzmann constant, and T is the absolute temperature. The followingequation can be extracted from equation (3):V1={ln(I1/IO)}n×k×T/e+I1×Rs(I1<Ith)  (4)

In general, when a semiconductor layer performs laser oscillation, theactive layer voltage (junction potential) is fixed at the thresholdvoltage, therefore the element voltage is given byV2={ln(Ith/IO)}n×k×T/e+I2×Rs(I2>Ith)  (5)

In this case, the first term serves as a constant for the current.Assume here that optical coupling is controlled by the same elements,and the state is switched between the laser oscillation state andnon-oscillation state, as shown in FIG. 6. Further, I1=L2=Lb is replacedwith the above-mentioned V1 and V2, and the difference between V1 and V2is set to ΔV, thereby acquiring the following equation:ΔV={ln(Ib/Ith)}n×k×T/e  (6)

ΔV is equal to the difference (Voff−Von) between Voff and Von. In asemiconductor laser element, if the state can be switched between thelaser oscillation state and non-oscillation state, with the currentflown therethrough kept constant, this means that the voltage of theelement varies. In contrast, if the element bias voltage is keptconstant, the current flowing through the element varies.

This phenomenon serves as the principle of the laser-induced opticalwiring apparatus of the embodiment. Namely, two active layers eachhaving one side functioning as a reflection mirror are optically coupledinto a laser oscillator, whereby the laser oscillation state of theentire system is varied by a variation caused in one of the activelayers, which results in a variation in the other active layer. In otherwords, when the two active layers are located separately, a variationcaused in one of the active layers is transmitted to the other activelayer, with the result that some sort of variation can be extracted fromthe other active layer. Thus, the laser oscillator can have a signaltransmission function.

A description will be given of an operation method example for use inthe embodiment of FIG. 1. Firstly, Ib/2 is supplied as a bias current tothe electrodes 16 a and 16 b to thereby set the system in the laseroscillation state (as indicated by the laser oscillation lines of FIG.6). Subsequently, a signal is supplied to one of the electrodes 16 a and16 b. For instance, −Ib/2 as a signal is supplied to the electrode 16 a,thereby offsetting the bias current supplied to the electrode 16 a. Atthis time, the laser oscillation of the system is stopped, and thevoltage at the electrode 16 b increases from Von to Voff. Assuming thatIth=10 mA and Ib=30 mA, the threshold current and bias current of theactive layers 12 a and 12 b are 5 mA and 15 mA, respectively. Further,assuming that the diode constant (n) is 2, ΔV (Voff−Von) is about 57 mV.

The above-described signal supply may also be made to the electrode 16b. In this case, a signal voltage occurs at the electrode 16 a. Namely,in the above bias- and signal-supply process, a signal voltage of about50 mV occurs at the electrode other than that to which a signal issupplied. The active layer of the electrode, to which a signal issupplied, is switched from the gain-on state to the gain-off state andfunctions as an optical switch. Thus, in the embodiment of FIG. 1, oneof the electrodes functions as an optical switch, and the otherelectrode functions as an optical-gain/signal-receiving section. Thesefunctions can be switched from each other, namely, bidirectionaltransmission can be achieved.

The limit set to the phenomenon that a variation in one active layerappears as a variation in the other active layer will be described.Lasers utilize stimulated emission phenomenon, and it is an essentialrequirement to apply light to an activated laser medium. Accordingly,when two active layers are located separately and a laser oscillator isformed therebetween as in the first embodiment, stimulated emissionoccurs, delayed by the time corresponding to the optical transmissiontime between the active layers (or between the mirrors). This means thatthe time corresponding to the delay time is required for starting thelaser oscillation operation. Therefore, in the laser-induced opticalwiring apparatus of the embodiment, it is difficult for the laseroscillator to operate in a shorter time than the time required for lightgoes round the laser cavity.

However, in the example of FIG. 1, assuming that the effectivereflectance of the active layers and optical waveguide is 3.5, and thelaser oscillator length is about 1 mm, the time required for light tomake a circuit of the system is about 23 ps, and the maximum responsespeed is about 40 GHz. Namely, signals of about ten and several GHz canbe sufficiently processed. In the case of non-return-to-zero (NRZ)signals for general logic data, signals of about 20 Gbps can beprocessed.

As described above, in the first embodiment, the optical waveguide 13that optically couples the first and second mirrors 18 a and 18 b isprovided on the substrate 11, and the first and second active layers 12a and 12 b, which cooperate to form a laser oscillator, are providednear the mirrors 18 a and 18 b, respectively, whereby the emissionelements and optical waveguide serve as base elements for opticalwiring. Since no dedicated light receiving elements are necessary, andthe system is designed only for the laser operation. Strict designingfor optical transmission, such as setting of opticaltransmission/receiving levels based on the minimum receiving sensitivityor optical coupling efficiency, is not required.

Optical transmission is essentially transmission of waveforms even ifthe data is digital one. Thus, it is regarded as transmission of analogdata. Therefore, it should be elaborately designed in order to preventnoise from mingling into the data. The optical wiring used in thisembodiment, the signals represent whether the laser emits light or notin the system. Hence, the transmission is essentially digital-datatransmission. Errors, if any in the signals, can therefore be muchreduced.

Accordingly, the required structural elements for optical wiring aresignificantly simplified to thereby reduce the factors of variation orfailure. Further, the operational margin of the system is significantlyenhanced to thereby remarkably reduce the frequency of occurrence ofdefects in characteristics. Namely, the characteristic reproducibilityor reliability of optical wiring can be drastically enhanced, and thepractical utility of LSI on-chip optical wiring can be greatly enhanced,which significantly contributes to high integration of, for example,information communication devices.

Further, in the first embodiment, the active layers 12 a and 12 b areprovided near the mirrors 18 a and 18 b, respectively, and each of theactive layers 12 a and 12 b serves as an optical gain unit for providinga laser oscillator, and also as a signal receiving unit for detectingemission states. As a result, bidirectional signal transmission ispossible.

Second Embodiment

FIG. 7 shows a laser-induced optical wiring apparatus according to asecond embodiment. The second embodiment includes a circuit equivalentto the laser-induced optical wiring apparatus of FIG. 1, and aperipheral circuit. However, it should be noted that the method foroperating the apparatus is not limited to that described below, like theabove-described operation method.

In FIG. 7, the circuit including elements 12 a, 13 and 12 b and enclosedby the broken line is equivalent to the first embodiment. Bias resistorsRd may be located on or outside the substrate of the apparatus ofFIG. 1. In the second embodiment, assume that the bias voltage appliedto the bias resistor Rd connected in series to the active layer 12 a(elements 12 a, 14 a and 11 constitute a pn-junction diode) is Vd, thebias current flowing through the bias resistor Rd is Id, the voltageapplied at the connection terminal between the bias resistor Rd andactive layer 12 a is Vsa, and the current flowing from the terminal Vsais Isa. The oscillation threshold values acquired when the same currentis flown through the active layers 12 a and 12 b are set as Ith and Vththat serve as laser oscillation characteristics. Namely, assume that thecurrent corresponding to the oscillation threshold values is Ith/2 foreach active layer 12 a, 12 b.

As an operation example of the circuit, assume that Id is set to a valueslightly lower than the threshold current value, e.g., 0.95×Ith/2(=0.475 Ith), and that the signal transmission side flows a current Issufficiently greater than Ith. In this state, when Is=0 (Isa=Isb=0), Vsaand Vsb is substantially equal to Vth. At this time, a current ofIsa=2Ith as a signal is supplied to, for example, the active layer 12 a,whereby although the active layer 12 b is supplied with a current lowerthan the threshold value, the entire system assumes a laser oscillationenabled state as a result of the application of light from the activelayer 12 a.

Upon occurrence of laser oscillation, the effective threshold value (thecurrent value reaching the quantity of light corresponding to theoscillation threshold value) of the active layer 12 b is reduced. Thisstate is equivalent to the case where a bias current higher than thethreshold value is supplied to the active layer 12 b. Accordingly, theelement voltage is reduced because of the principle previously describedreferring to FIG. 6. Namely, Vsb is reduced as a result of the supply ofIsa, and a variation in Vsb is extracted to realize the transmission ofa signal from the active layer 12 a to the active layer 12 b. Incontrast, Vsa can be reduced as a result of the supply of Isb, therebyrealizing signal transmission in the opposite direction.

Furthermore, Id may be preset to a value higher than Ith/2, e.g., Ith(the entire current is 2Ith) to make the system perform laseroscillation from the beginning, and Isa and Isb may be set to a negativecurrent level (e.g., −Ith) that can stop laser oscillation. In thiscase, the phase of a signal output is opposite to that of the signaloutput acquired when a bias not higher than the threshold value issupplied.

Third Embodiment

Although the first and second embodiments employ a linear opticalwaveguide, the optical waveguide may be angled as shown in FIG. 8. Inthis case, the optical loss of the optical waveguide 13 is the sum ofabsorption losses αt and Lt and a loss due to the angled portion, andthe influence of the optical loss appears as an increase in the laseroscillation threshold value due to the angled portion.

Alternatively, the optical waveguide may comprise two perpendicularlyintersecting waveguide components as shown in FIG. 9. Specifically, inFIG. 9, there are provided a first optical waveguide 13 a similar to theoptical waveguide 13, and a second optical waveguide 13 b perpendicularthereto. Third and fourth mirrors 18 c and 18 d are provided at theopposite ends of the second optical waveguide 13 b, and third and fourthactive layers 12 c and 12 d and electrodes 16 c and 16 d are providednear the mirrors 18 c and 18 d, respectively.

Even if the two optical waveguides 13 a and 13 b (extending between themirrors 18 a and 18 b and between the mirrors 18 c and 18 d)perpendicularly intersect each other, the same signal transmission asthe above can be realized. This is an application of the fact thatperpendicularly intersecting light beams do not interfere with eachother. When the two waveguides 13 a and 13 b perpendicularly intersecteach other, they can function as independent optical wiring members.Note that it is necessary to make the waveguides intersectperpendicularly.

As described above, in the laser-induced optical wiring apparatus of theembodiment, the essential function of the optical waveguide 13 does notchange because of the configuration, wiring pattern, perpendicularintersecting state, etc.

Fourth Embodiment

FIG. 10 shows a fourth embodiment of the invention. As shown, the fourthembodiment differs from the third embodiment shown in FIG. 9 in that theformer employs an active layer, which is located at the intersection ofthe perpendicularly intersecting wiring members and has an additionalfunction. Specifically, an electrode 16 e is provided on theintersection, and an active layer (not shown) similar to the activelayers 12 a to 12 d is provided below the electrode 16 e. Further, twolaser-induced optical wiring apparatuses, which utilize a laseroscillator formed of the three electrodes 16 a, 16 e and 16 b, and alaser oscillator formed of the three electrodes 16 c, 16 e and 16 d, aresynthesized using the central active layer (located below the electrode16 e).

The operation of a laser oscillator formed of three electrodes (e.g., 16a, 16 e and 16 b) will be described. This laser oscillator can emitsignals from the three electrodes, like the previously describedtwo-electrode laser-induced optical wiring apparatus. Further, a signalinput to one of the electrodes can be received by the other twoelectrodes. This laser oscillator is operated such that the operationcircuit shown in FIG. 7 is applied to the three active layers to operatethem in the same manner as in FIG. 7.

A description will now be given of the operation of two laser-inducedoptical wiring apparatuses—one apparatus using a laser oscillator formedof three electrodes 16 a, 16 e and 16 b, and the other using a laseroscillator formed of three electrodes 16 c, 16 e and 16 d. The couplingoperation of the two laser-induced optical wiring apparatuses can berealized via the active layer provided below the electrode 16 e. Forinstance, when the electrode 16 e is used as a transmission electrode,information from the electrode 16 e can be transmitted to all theremaining four electrodes. Further, information (signal) transmittedfrom the electrodes 16 a, 16 b, 16 c and/or 16 d can be received by theelectrode 16 e. In addition, signal transmission can also be performedbetween the two laser-induced optical wiring apparatuses.

Thus, the common active layer provided between the optical waveguides asshown in FIG. 10 enables transmission between them or optical wiringbetween a large number of points.

Fifth Embodiment

FIG. 11 shows a fifth embodiment of the invention in which a surfaceplasmon waveguide is employed as the optical waveguide. In thisembodiment, the laser active layer is formed of part of an Si substrate,and the optical waveguide is formed of a metal thin film. Specifically,in FIG. 11, reference number 21 denotes an Si substrate, referencenumber 22 denotes an SiO₂ cover, reference numbers 23 a and 23 b denotep-wells, reference numbers 24 a and 24 b denote n-wells, referencenumbers 25 a and 25 b denote n-electrodes, reference numbers 26 a and 26b denote p-electrodes, reference number 27 denotes a surface plasmonguide (metal thin film), and reference numbers 28 a and 28 b denotereflection mirrors.

Assume here that the electrodes 25 a, 25 b, 26 a and 26 b are formed ofAl, and the surface plasmon guide 27 is formed of Au and has a thicknessof 40 nm, a width of 2 μm and a length of 100 μm. Below the Au thin filmas the plasmon guide 27, an insulation film formed of SiO₂ and having athickness of 20 nm is provided. Si emission sections (laser activesections) are formed of parts of the substrate 21 located between thep-well 23 a and n-well 24 a and between the p-well 23 b and n-well 24 b,and perform optical re-coupling when carriers are injected from both then- and p-wells.

When the p-wells or n-wells are formed, a dopant paste, mixed with SiO₂particles with a particle diameter of about 10 nm, is coated by spincoating and thermally diffused. As a result, an uneven diffusion frontof several nm to several tens nm is formed, thereby accelerating opticalre-coupling utilizing the carrier confining effect by the nano-sizeunevenness. Further, a rare-earth dopant may be injected into the Siemission section to make it perform rare-earth emission, or nano-size Siparticles coated with an SiO₂ film of several nm may be provided toperform fine-particle Si emission.

The surface plasmon is a kind of polariton acquired by coupling light tovarious types of polarized waves. Namely, it is a light propagation modeon a metal surface, in which light is coupled to free-electron shiftpolarization. In general, it is called surface plasmon polariton (SSP).As shown in FIG. 12, SSP light is confined in a zone having the metalboundary as its center, and if the Si emission section is positionedwithin the range of the photoelectric field distribution of SSP, it canperform stimulated emission.

In the embodiment of FIG. 11, respective diodes are formed between theelectrodes 25 a and 26 a and between the electrodes 25 b and 26 b, andwhen a forward current is flown through the diodes, the diodes emitlight. Further, when a current is flown between the electrodes 25 a and26 a and between the electrodes 25 b and 26 b, the opposite activelayers emit light, and laser oscillation using the mirrors 28 a and 28 bis performed. In this state, signal transmission is performed in thesame way as in the above-described embodiments.

In general, a waveguide mode exists at the boundary of a metal anddielectric. Further, in the case of a metal thin film, a waveguide mode,in which SPPs at the obverse and reverse sides of a metal are coupled,exists as shown in FIG. 13. The curves in FIG. 13 indicate wave surfacesof the SPP waveguide mode. There is a case where the obverse-side SPPand reverse-side SPP have the same phase, and a case where they havedifferent phases. Further, as shown in FIG. 14, the waveguide mode inwhich two SPPs are coupled exists even in a fine gap between thin metallayers. These waveguide structures may be used in accordance with theplace, peripheral conditions, etc.

(Modification)

The invention is not limited to the above-described embodiments.Although various structural components are employed in the embodiments,they are merely examples, and another means (material, size, etc.) maybe used in place of each component, without departing from the scope ofthe invention. Further, the materials, configurations, arrangement,etc., are merely examples. Some of the embodiments may be combinedappropriately.

Specifically, although in the embodiments, optical gain sections areprovided at the opposite ends of the optical waveguide, one of them maybe replaced with an optical switch 31 as shown in FIG. 15. Also in thiscase, by varying the optical loss of the optical waveguide 13 using theoptical switch 31, the laser oscillation state can be varied, therebyproviding the same advantage as the above-described embodiments. In thiscase, however, a signal voltage is applied in only one direction (i.e.,from the optical switch 31 to the optical gain section 21), whichdiffers from the above embodiments in which the voltage can be appliedin opposite directions.

In addition, although in the embodiments, the optical gain sectiondetects a change in laser oscillation state, a photodetector may beprovided for detecting the light guided through the optical waveguide tothereby detect a change in laser oscillation state. For example, aphotodetector 32 may be provided outside the mirror 18 a to detect thelight passing therethrough, as shown in FIG. 16. The location of thephotodetector 32 is not limited to this. It is sufficient if thephotodetector can detect the light guided through the optical waveguide.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

1. A laser-induced optical wiring apparatus comprising: a substrate; afirst light-reflecting member and a second light-reflecting member,which are provided on the substrate separately from each other; anoptical waveguide provided on the substrate, the optical waveguideoptically coupling the first light-reflecting member and the secondlight-reflecting member to form an optical resonator; a first opticalgain member provided across a portion of the optical waveguide; and asecond optical gain member provided across a portion of the opticalwaveguide separately from the first optical gain member, wherein thefirst optical gain member and the second optical gain member forms alaser oscillator along with the first light-reflecting member and thesecond light-reflecting member, wherein: when the first and secondoptical gain members are activated, the laser oscillator performs laseroscillation; when a gain of one of the first optical gain member and thesecond optical gain member is changed by an input signal, a total gainof an optical path extending between the first light-reflecting memberand the second light-reflecting member is changed to change a laseroscillation state of the laser oscillator formed by the first opticalgain member and the second optical gain member; and a change in thelaser oscillation state is detected by the other of the first opticalgain member and the second optical gain member.
 2. The apparatusaccording to claim 1, wherein the first optical gain member and thesecond optical gain member are activated when a current is flown througheach of the first optical gain member and the second optical gainmember, and a change in the laser oscillation state of the laseroscillator is detected when a voltage at a corresponding one of thefirst optical gain member and the second optical gain member or acurrent flowing through the one of the first optical gain member and thesecond optical gain member is changed.
 3. The apparatus according toclaim 1, wherein at least a portion of the optical waveguide extendingbetween the first light-reflecting member and the secondlight-reflecting member is angled.
 4. The apparatus according to claim1, wherein the optical waveguide is a surface plasmon waveguide.
 5. Theapparatus according to claim 1, wherein: in a transmitting mode, each ofthe first optical gain member and the second optical gain member changesits gain in accordance with an input signal to change a laseroscillation state of the laser oscillator; and in a receiving mode, eachof the first optical gain member and the second optical gain memberkeeps a state of its activation constant to detect, as a receivedsignal, a change in activated carrier consumption corresponding to achange in its laser oscillation state, wherein said each of the firstoptical gain member and the second optical gain member serves as both atransmission member and a reception member to enable bidirectionaltransmission or multipoint transmission.